The invention relates to a system for charging a rechargeable battery of a portable unit in a rack, and more particularly to a system comprising a detection circuit which detects the presence of the unit in the rack, transfer means which are connected to a supply circuit of the rack and to a charging circuit of the unit and the battery, and which, after placement of the unit in the rack, charges the battery with energy from the supply circuit via the charging circuit, and a transmission circuit of the unit, which transmission circuit is connected to the battery and which, after placement of the unit in the rack, transmits a message via a wireless path to a control circuit of the rack.
Such a system is disclosed by the Dutch Patent Application 9002677, which was filed on Dec. 5 , 1990 in the name of the Applicant and which, at the time of filing of the present application, had not yet been laid open for inspection by the public. This earlier described system is a presence detection system for detecting the presence of a portable transmission unit in a rack. The transmission means comprises a pair of contacts of the compartment of the rack which are connected to the supply circuit, and a pair of contacts of the portable unit which are connected to the charging circuit. The contacts are arranged in such a way that, if the unit is placed in the rack, a current passes via the contacts from the supply circuit to the battery for the purpose of charging the battery. In this earlier described system the detection circuit is a detection circuit of the portable unit and, in its simplest form, comprises a switch. After the detection circuit has detected the placement of the unit in the rack, the transmission circuit of the unit transmits a message to the control circuit of the rack. The wireless transmission path may be an induction path with a coil in the rack and a coil in the portable unit, which coils form an induction coupling after placement of the unit in the rack. The message contains an identification number assigned to the portable unit.
A system of the type mentioned in the preamble is also disclosed by the Dutch Patent Application 9001318, which was submitted on Jun. 11, 1990 in the name of Applicant and which corresponds to the U.S. patent application Ser. No. 711,904 filed on Jun. 7, 1991, now U.S. Pat. No. 5,194,856, and to the European Patent Application 91201255.6 filed on May 24, 1991. None of these three patent applications had been laid open for inspection by the public at the time of filing of the present application. This earlier described system is also a presence detection system for detecting the presence of a portable transmission unit in a compartment of a rack. In the case of this system, too, the transfer means comprises the same type of contacts in a similar arrangement as explained above. This earlier described system detects the presence of a portable unit in a compartment of the rack by emitting, by means of a transmission means, an interrogation or scanning signal from each compartment and by waiting for a response signal originating from any portable unit which may be present in the compartment, which response signal contains an identification number assigned to the unit. Emission of the scanning signal can take place sequentially, i.e. consecutively for all compartments, or whenever a presence detection means of a compartment, for example a switch, has detected a movement of a unit in the compartment. Here also, the wireless transmission path for the response signal may be an induction path.
The earlier described systems have the drawback that the charging of a battery of a portable unit via the contacts will not always proceed satisfactorily, for example, because the contacts may be dirty and/or the unit has not been properly placed in the rack and the contacts are not touching each other. Furthermore, the fitting of contacts of this type, in particular to the housing of a portable unit, is fairly inconvenient and expensive. Furthermore, the charging rate is fixed, and thus independent of the state of a battery to be charged. Therefore, it is always necessary to choose a safe, relatively slow charging rate. Consequently, it is possible that at the time when the portable unit is removed from the rack, the battery will be insufficiently recharged for relatively long subsequent usage.